This invention relates generally to a hydraulic control system, and more specifically to a variable volume, variable pressure hydraulic pump connected to a hydraulic motor which drives the motor at a constant RPM regardless of the load placed on the motor. The motor is connected to a generator, or the like, for which it is essential to maintain a constant RPM in order to provide proper cyclic electrical generation.
In the past, hydraulic control systems have utilized complex pressure lines and pressure valves and elaborate dumping systems in order to achieve some sort of constant RPM output from the hydraulic motor. An example of such a hydraulic control device would be U.S. Pat. No. 3,246,471 issued to W. B. Goodale, Apr. 19, 1966, which shows a pump and motor connected together utilizing an adjustable flow restricting valve in the pump discharge line. Differential pressure is utilized through a flow control valve in order to adjust the system for changes in input or output demands.
Applicants' provide a much less complex device than is shown in the prior art by utilizing a constant volume control valve in the pump discharge line which controls the volume of flow to the motor thus establishing and maintaining a constant RPM output of the motor. A pressure regulating piston adjusts the fluid displacement of the pump to regulate pump output for increased pressure demands which may be made on the motor required by changes in demand to the generator which the motor is driving.
Thus, Applicants' device provides a hydraulic control system of increased reliability and decreased complexity.